1. Field of the invention
The present invention relates in general to monitoring connection quality. In particular the present invention relates to monitoring connection quality in a communication system having split architecture.
2. Related art
A communication system can be seen as a facility that enables communication between two or more entities such as user equipment and/or other nodes associated with the system. The communication may comprise, for example, communication of voice, data, multimedia and so on. The communication system may be circuit switched or packet switched. The communication system may be configured to provide wireless communication. Communication systems able to support mobility of communications devices across a large geographic area are generally called mobile communications system. In cellular communication systems a communications device typically changed the cell via which it communicates. Some examples of a cellular communications system are the Global System for Mobile Telecommunications (GSM) and the Universal Mobile Telecommunications System (UMTS).
Traditionally public mobile communications systems have used licensed radio frequencies, which means use of a radio frequency band allocated to mobile telephone networks by national or international authorities or organizations. Recently, alternative methods for accessing mobile communications systems have been introduced. For example, a wireless local area network (WLAN) or any other wireless network may be operably connected to a mobile communications system, typically via a packet-switched network and a gateway. A communications device may establish a packet data connection to the gateway, which then provides access to the mobile communication system for the communications device by relaying user-plane data and control-plane signaling between the communications device and the mobile communications system. The wireless network may use a radio frequency different from the frequency band used by a mobile communications system, and typically the communication protocols used in the short-range wireless network are different from the communication protocols used in the mobile communications system. Unlicensed Mobile Access (UMA) and the 3rd Generation Partnership Project (3GPP) WLAN Interworking are examples of proposals for providing access to a mobile communications system via a wireless network.
FIG. 1 shows schematically access to a mobile communications system via a traditional cellular access network 110 and via an alternative access network 130. The cellular access network 110 has transceiver network elements 111 connected to control network elements 112. FIG. 1 shows two transceiver network elements 111a, 111b as examples. In GSM, the transceiver network elements are called base stations and the control network elements are called base station controllers.
The core network 120 of the mobile communications system contains various network elements. In the following, the names of the GSM network elements and General Packet Radio Service (GPRS) network elements are used, but it is appreciated that in mobile communications network in accordance with other standards the names may be different. The core network 120 contains mobile switching centers 121 for supporting circuit-switched connections, a home location register 122 for storing subscriber information, and GPRS support nodes. The GPRS support node include at least a serving GPRS support node (SGSN) 123 and a gateway GPRS support node (GGSN) 124. Packet data connections to further networks are made via the GGSN.
Mobile communications systems and their cellular access networks 110 typically support transfer of connections from on transceiver network element 111a to a further transceiver network element 111b. The transfer of connection is typically called a handover. When a terminal 101 moves, it may enter the coverage area of a further transceiver network element. Depending, for example, on the signal quality and amount of terminals in the area, it may be advantageous to make a handover and start to use the further transceiver network element. A user of the terminal typically should not notice the handover, as the aim is to perform the handover without breaks in the connectivity.
FIG. 1 shows also an access network 130 containing transceiver elements 131, which are often called access points. Some examples of technologies, using which the access network 130 may be implemented, are Wireless Local Area Networks (WLAN) and Bluetooth. Other wireless networks or ad hoc networks may also be used. Typically the access network 130 does not support handovers from one access point to another, but connections are typically set up again if a terminal moves outside the coverage area of one access point.
The access network 130 may be used as an alternative access network to the mobile communication network. In accordance with the Unlicensed Mobile Access (UMA) architecture, the access network 130 is connected via a packet data network 140 to an UMA network controller (UNC) 151. The UMA network controller 151 has various interfaces to communicate with the relevant network elements in the core network 120. Typically there is needed an additional authentication server 152 in the core network 120, providing access to the subscriber information in the HLR 122 for the UNC 151. In FIG. 1, the authentication server 152 is shown to be an Authentication, Authorisation and Accounting (AAA) server.
FIG. 2a shows in more detail the UMA functional architecture. In the UMA network controller 151 (or in connection with the UNC 151) there is typically a security gateway 153. This security gateway 152 is typically responsible for authenticating the terminal 101 (or the user thereof) using information available in the HLR 122 via the authentication server 152. The security gateway 152 is responsible also for data security (for example, authentication, encryption and/or data integrity) of the data transfer between the terminal 101 and the security gateway 152. This data transfer includes signaling data and user data. The user data may be packet data or circuit-switched data. The UMA network controller 151, in turn, is responsible for various signaling towards the core network 120, more particularly towards the mobile switching centers 121 and serving GRPS support nodes 123.
The UMA network controller 151 appears to the core network 120 as a base station subsystem of the access network 110. In other words, the core network 120 need not know that the terminal 101 is accessing the core network 120 via an alternative access network 130.
Recently Voice over IP (Internet Protocol) has become more and more important. Voice over IP refers to various techniques for carrying speech over packet data (most often over IP) instead over circuit switched connections. UMA technology differs from other voice over IP technologies by allowing seamless handovers for speech calls between cellular access networks and alternative access network. End users are able to move, for example, between WLAN access point coverage and cellular network coverage without losing the call connection. The seamless handovers are facilitated by the same link layer call control and mobility management procedures used in the WLAN access network (under the control of the UNC) and in the cellular access network.
FIG. 2 shows schematically one example of implementing the UMA access. In FIG. 2, there is a security gateway 253 responsible for securing the data transfer (user data and signaling data) between the terminal 101 and the security gateway 253. This security gateway 253 is typically operatively connected to the subscriber information store (HRL 122 in FIG. 2) of a mobile communications system via an authentication server 152 for authenticating the terminal 101 towards the mobile communications system before allowing access. The data transfer between the terminal 101 and the security gateway 253 is typically secured using the IPSec protocol suite.
The signaling UNC 251 is responsible for signaling and for packet data transfer. In the case of a GSM network, the signaling UNC 251 is connected to the MSC via a modified A interface. There may be a MSC server 254 in between the UNC 251 and the MSC 121 to implement the modified A interface.
Data to be carried by circuit-switched connections is directed from the security gateway 253 to a media gateway MGW 255. This media gateway 255 typically responsible for transcoding speech codecs used in the UMA network 130, 140 and in the operators core network. As an example, transcoding may occur between GSM Adaptive MultiRate Full Rate (GSM AMR FR) and G.711 Speech codec.
Speech quality within GSM networks has traditionally been good. Also in third generation cellular network a considerable amount of effort is put into ensuring speech quality. When the alternative access networks become more popular, the end users will inevitably compare the speech quality provided by the alternative access networks to the speech quality provided by traditional access networks. To meet the users' expectations, it is important to try to provide to good speech quality in the alternative access networks or, if needed and there is coverage, a handover to traditional access network.
Most likely UMA compliant terminal 101 will have some manual configuration possibilities for defining preferred radio access technologies. This way, if the terminal 101 is in the coverage area of both the access network 110 and the alternative access network 130, the terminal 101 may automatically choose the preferred radio access technology.
Regarding the perceived speech quality, many factors affect the speech quality the user perceives. As example, the audio/speech codec, the design of the radio interface, terminal design, and the quality of the connection all have an impact to the perceived speech quality. The design of the radio interface and the design of the terminal are fixed in a system. In theory, the selected audio codec thus has the greatest impact, but in practice the audio codec should be selected to match the available channel (connection) quality. It is therefore of utmost importance to have information about the quality of the connection over which speech/audio information is transmitted.
Some factors affecting the quality of the connection are end-to-end delay, variations in the end-to-end delay (itter), variations in the jitter (wander), packet loss. Further factors affecting the perceived speech quality, in addition to the audio codec, are effective echo cancellation and voice activity detection.
To cope with changes in the quality of the connection and/or with the received speech quality, the UMA specifications define a procedure called Uplink Quality Indicator. The purpose is to inform the user (terminal) that the quality for the user plane connection has changed. An UMA compliant terminal may, upon receiving an Uplink Quality Indicator, to trigger handover or network selection from the UMA network to a traditional access network in order to achieve better quality of service. An UMA terminal typically cannot monitor quality of the uplink connection without assistance from the network.
It is appreciated that in the configuration shown in FIG. 2, the signaling UNC 251 is unable to inform the terminal about the quality of the connection for the speech data. The Uplink Quality Indicator procedure thus cannot be effectively used. A terminal may thus remain in a UMA network even if a better quality connection would be achievable by making a handover to a traditional access network.
One way to overcome the problem in connection with FIG. 2 is to provide a guaranteed quality of connections in the network 140. Current IP networks, however, typically do not provide a guaranteed quality of service or handle quality of service requirements. IP networks are typically best effort networks. Differentiated Services (Diffserv) is an approach which could be applied in the network 140, but this would mean that all relevant network elements should be updated to support Diffserv. Diffserv is discussed, for example, in Internet Engineering Task Force's (IETF) Request For Comments (RFC) 3260 “New Terminology and Clarifications for Diffserv”. Intergrated Services (Intserv) is another approach, but it is not in practice used. Intserv is discussed, for example, in RFC 1633 “Integrated Services in the Internet Architecture: an Overview”.
One option to overcome the problem is to rely on the user manually re-configuring the terminal to using a traditional access network instead of the alternative access network. This approach, however, requires that the user realizes that the lowered quality of speech is due to problems with the alternative access network and, furthermore, the user has to be able to do the manual re-configuration. Furthermore, a connection would not be handed over without interruptions in accordance with current specifications.
It is appreciated that although the previous description refers mainly to UMA, similar problems may arise in connection with other similar techniques.
Embodiments of the present invention aim to address at least some of the problems discussed above.